A shear-type mechanism can be provided on a loading apron of a tunnel and gallery excavator for displacing excavated detritus as it is deposited on the apron, onto a conveyer carrying the detritus rearwardly as the excavator is advanced. This mechanism can comprise a crank disk, a crank lever, a shearing rake or scraper, and a guide member or pivoted link.
The disk is rotatably driven about its axis of rotation on the loading apron in a single direction of rotation and the crank lever is connected to a pivot mount or pin on the mounting disk.
The crank lever is pivotally connected by a lever arm to the guide member or link, which is pivotally attached behind the eccentric carrying crank disk on the loading apron with regard to the forward travel direction of the tunnel and gallery excavator. The rake is connected to the crank lever.
These parts form a lever mechanism having pivot joints, and are so constructed with respect to the lever arm of the crank lever that the load occuring is taken up reliably and properly acted upon. The load is often increased when large broken stones are involved. The device on which the loading mechanism is mounted may be any tunneling machine such as a gallery excavator or shaft excavator.
Heretofore the shear rake has generally been a rigid extension of the connecting member projecting with the eccentric pivot over the attachment point of the connecting member. The lever mechanism is substantially all in a plane with the double-ever connected to the eccentric carrying crank disk, and is kinematically defined by the length of the lever arm, the eccentric pivot radius, and the mounting point of the guide member on the loading apron.
An analysis of the kinematic cooperation shows that the shearing rake engages very far to the front in the travel direction of the tunnel and gallery excavator, but that it sweeps over a comparatively small region transverse to the travel direction of the tunnel and gallery excavator. An undesirable ratio of the width of the loading mechanism to the total depth of the loading mechanism in the forward travel direction exists in the loading mechanism of the prior art.
On the other hand, practice requires a loading mechanism which is comparatively wide, in order to be able to extend the range of action of an excavator which is, for example, mounted on tracks. That is hardly possible with prior art mechanisms, since the length of the cutting or digging tool must increase in the forward direction of travel of the excavator in the same proportion.
The cutting mechanism must be mounted with its cutting head over the forward edge of the loading apron at the front, drive edge of the excavator. Furthermore, widening of the apron and detritus pickup range is desirable even where undercuts below the apron are desirable.
One prior art cutting tool projects so far that the center of gravity of the tunnel and gallery excavator changes, and a counterweight is required on the end of the machine opposite the cutting tool which is expensive and impairs the versatility of the tunnel and gallery digging machine.